1. Field of the Invention
The present invention relates to an inductance device which is properly used as a choking coil, an inductor, or the like, and a manufacturing method thereof.
2. Description of Related Art
Conventionally, as a choking coil, art is known in which a coil is wound around a center core (drum core) which is composed of a magnetic material such as a ferrite, or the like, and a side case (accommodation case) is arranged around the center core (see, for example, Patent Document 1: Japanese Unexamined Patent Application, First Publication No. H10-199730, Patent Document 2: Japanese Unexamined Patent Application, First Publication No. H10-241969, Patent Document 3: Japanese Unexamined Patent Application, First Publication No. 2000-150244, Patent Document 4: Japanese Unexamined Patent Application, First Publication No. 2001-35723, and Patent Document 5: Japanese Unexamined Patent Application, First Publication No. 2001-345225).
As the manufacturing method of such a choking coil, for example, methods as described below are used.    (1) A hollow center coil in which a conducting wire is wound so as to form a hollow portion along a center axis line is inserted into the center core, and the center core into which the hollow center coil is inserted is attached to the side case.    (2) The coil is formed by winding the conducting wire around an outer periphery of the center coil, and the center core around which the coil is wound is attached to the side case.
However, in method (1), when the hollow center coil is inserted into the center core, it is difficult for the hollow center coil to be attached exactly to the outer periphery (side surface) of the center core, so that there is a problem in which an air gap (clearance) tends to inevitably arises between the center core and the coil. Therefore, it is difficult to avoid decreasing the efficiency (performance) of the coil due to the air gap. Moreover, in order to manufacture the coil with the core, two processes of the manufacturing process of the hollow center coil and the insertion process for the center core are needed, which is inadequacy in view of workability.
Moreover, in method (2), in order to wind the coil around the periphery of the center core, it is necessary to rotate the center core with supporting it on its axis. Because of this requirement, a special manufacturing apparatus is needed and productivity of the coil is decreased. Moreover, when the center core has a shape such as a square sleeve shape having plane surface portions on the side surfaces, although the conducting wire which is wound around the center core contacts a ridgeline of the center core, the conducting wire extends in a round shape toward the outside at the plane surface portions, to generate air gaps (clearances) between the center core and the coil. Therefore, it is difficult to avoid decreasing the efficiency (performance) of the coil due to the air gap.
Moreover, because a core which consists of ferrite is very fragile and easily broken, careful handling is required, and a problem occurs in which productivity or yield is decreased.
Incidentally, in an inductance device which is used as a choking coil, an inductor, or the like, a ferrite core or a powder pressed core is conventionally used as the wound core (center core) of the coil, a case (ring core such as a pot shaped core, or the like) in which the coil is accommodated, or the like.
Among these, a powder pressed core can be obtained by a method in which magnetic powder is mixed with binder resin, and press molding is performed using a metal mold, or the like (see, for example, Patent Document 6: Japanese Unexamined Patent Application, First Publication No. 2001-274029).
However, in order to perform the press powder molding of the core, it is necessary to perform the press molding at considerably high temperature and high pressure. Therefore, a problem occurs in which manufacturing equipment becomes large in size, and expense and cost increase.
Moreover, the inductance device needs to be manufactured so that quality (inductance, and the like) is maintained within the range of a predetermined allowable error according to the use, the purpose, or the like thereof. When a powder pressing process is included in the manufacturing method of the inductance device, performing press molding of a formation including the magnetic powder and the binder with high temperature and high pressure may cause quality of the inductance device to change, and disparity of quality of the product to become higher. It is, therefore, difficult to manufacture products of which disparity of quality is small and precision is high, and thereby a problem occurs in which yield is decreased and cost is increased.